1. Field of the Invention
The present invention relates to a printed circuit board (PCB) with thin film switches for a keyboard and, more particularly, to a PCB with thin film switches for a keyboard and having a stable touching sensitivity.
2. Description of Related Art
A keyboard includes a base having an upper opening, a top cover, a printed circuit board (PCB), and multiple keys. The multiple keys are mounted on the top cover, and the top cover is mounted over the upper opening of the base. The PCB is mounted in the base and has multiple thin film switches corresponding to the multiple keys on the top cover. Therefore, when one key is pressed, the pressed key will touch the corresponding thin film switch on the PCB, and then the PCB will output an electronic signal to a computer connected to the keyboard.
With reference to FIG. 2, a conventional dual-layer PCB of the keyboard has an upper board (10), an insulating separation (30), a lower board (20) and multiple thin film switches. The lower surface (101) of the upper board (10) and the upper surface (201) of the lower board (20) respectively have multiple circuit lines (12, 13) (22, 23). The insulating separation (30) is positioned between the upper and lower boards (10, 20) and defines multiple through holes (31). The upper surface (301) of the insulating separation (30) abuts with the lower surface (101), and the lower surface (302) of the insulating separation (30) abuts with the upper surface (201).
The multiple thin film switches are mounted between the upper board (10) and the lower board (20), but only one thin film switch is shown in FIG. 2. Each thin film switch includes two thin conductive elements (40, 50) respectively formed on the upper and lower boards (10, 20). The two thin conductive elements (40, 50) are aligned with one of the through holes (31), and each is formed as a metal sheet. The two thin conductive elements (40, 50) are respectively connected to the circuit lines (12, 13) (22, 23).
The two thin conductive elements (40, 50) are separated by the insulating separation (30) and aligned with the corresponding through hole (31). When one key on the top cover of the keyboard is pressed, the two conductive elements (40, 50) corresponding to the pressed key touches with each other and are connected electronically through the aligning through hole (31) of the insulating separation (30). When the pressed force applied onto the key is released, the two thin conductive elements (40, 50) are disconnected electronically.
Since the thin conductive elements (40, 50) are formed on the upper and lower boards (10, 20), exposure surfaces of the thin conductive elements (40, 50) are easily shrunk to form to an uneven face in a curing procedure of fabricating the upper or lower board (10, 20). Thus, the uneven faces decrease a touching area between the thin conductive elements (40, 50) to make the touching sensitivity of the thin film switch not stable.
Therefore, the present invention provides a new printed circuit board with thin film switches of a keyboard to overcome the drawback of the conventional thin film switch.